Our overall objectives are the understanding of aortic metabolism as it relates to the development of atherosclerosis. Two enzymes will be studied. Cholesteryl esterase (EC 3.1.1.13) activity is present in an NH4Cl extract of aortic acetone powder. The extract possesses both synthetase (S) and hydrolase (H) activity. We propose to purify the enzyme and to examine the S/H ratio as a function of atherogenic diet, age species, and hypolipidemic drug administration. The other enzyme is N-acetyl-beta-D-hexosaminidase (EC 3.2.1.30) which exists in heat labile (A) and heat stable (B) forms. The A/B ratios in aorta will be determined by gel electrophoresis. In serum a hydrolytic reaction gives A/B ratios. The influence(s) of diet, drugs and various disease states on A/B ratios in aortas and sera of various species will be studied.